What caused the river to stink?
Oznayim la'Torah #1: The dead fish, as implied by the wording of the Pasuk. 1
Oznayim la'Torah #2: The water stank because it turned into blood 2 - and this was aggravated by the heat of the summer sun. 3
Oznayim la'Torah: This explanation maintains that the water only looked like blood, but was not really blood. Refer to 7:22:1:2.
Refer to 7:18:1:1. Oznayim la'Torah - And the fish dying was a separate issue - connected with the fact that the Egyptians, who did not eat meat, considered fish a major part of their staple diet. See Oznayim la'Torah.
Oznayim la'Torah (citing R. Bachye): As Makas Dam took place around Sivan time.
Why does the Torah write that the Egyptians could not drink the river water due to the stench? It is obvious that one cannot drink blood!
Bechor Shor (cited in Hadar Zekenim and Riva #1 to 7:17): Because it turned to blood only temporarily. When it returned to water, they could not drink it only because of the stench.
Da'as Zekenim (to 7:18) and Riva #2 (to 7:17): Because the water merely looked like blood. 1 If not for the stench, they would have been able to drink it.
